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Deciphering the Lyman-α emission line: towards the understanding of galactic properties extracted from Lyα spectra via radiative transfer modelling

Li, Zhihui and Gronke, Max (2022) Deciphering the Lyman-α emission line: towards the understanding of galactic properties extracted from Lyα spectra via radiative transfer modelling. Monthly Notices of the Royal Astronomical Society, 513 (4). pp. 5034-5051. ISSN 0035-8711. doi:10.1093/mnras/stac1207.

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Existing ubiquitously in the Universe with the highest luminosity, the Lyman-α (Lyα) emission line encodes abundant physical information about the gaseous medium it interacts with. Nevertheless, the resonant nature of the Lyα line complicates the radiative transfer (RT) modelling of the line profile. We revisit the problem of deciphering the Lyα emission line with RT modelling. We reveal intrinsic parameter degeneracies in the widely used shell model in the optically thick regime for both static and outflowing cases, which suggest the limitations of the model. We also explore the connection between the more physically realistic multiphase, clumpy model, and the shell model. We find that the parameters of a ‘very clumpy’ slab model and the shell model have the following correspondences: (1) the total column density, the effective temperature, and the average radial clump outflow velocity of the clumpy slab model are equal to the H I column density, effective temperature, and expansion velocity of the shell model, respectively; (2) large intrinsic linewidths are required in the shell model to reproduce the wings of the clumpy slab models; (3) adding another phase of hot interclump medium increases peak separation, and the fitted shell expansion velocity lies between the outflow velocities of two phases of gas. Our results provide a viable solution to the major discrepancies associated with Lyα fitting reported in previous literature, and emphasize the importance of utilizing information from additional observations to break the intrinsic degeneracies and interpreting the model parameters in a more physically realistic context.

Item Type:Article
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URLURL TypeDescription Paper
Li, Zhihui0000-0001-5113-7558
Gronke, Max0000-0003-2491-060X
Alternate Title:Deciphering the Lyman-α Emission Line: Towards the Understanding of Galactic Properties Extracted from Lyα Spectra via Radiative Transfer Modeling
Additional Information:© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2022 April 24. Received 2022 April 7; in original form 2021 November 7. Published: 30 April 2022. We acknowledge the anonymous referee for the detailed reading of the manuscript and constructive feedback. We thank Phil Hopkins for providing computational resources. MG was supported by NASA through the NASA Hubble Fellowship grant HST-HF2-51409 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. MG thanks the Max Planck Society for support through the Max Planck Research Group. Numerical calculations were run on the Caltech compute cluster ‘Wheeler,’ allocations from XSEDE TG-AST130039 and PRAC NSF.1713353 supported by the NSF, and NASA HEC SMD-16-7592. We also acknowledge the use of the the following software packages: Astropy (Astropy Collaboration et al. 2018), the SCIPY and NUMPY system (Harris et al. 2020; Virtanen et al. 2020). Data Availability: The data underlying this article will be shared on reasonable request to the corresponding author.
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51409
Max Planck SocietyUNSPECIFIED
Subject Keywords:line: formation – radiative transfer – scattering –galaxies: high-redshift – galaxies: ISM
Issue or Number:4
Record Number:CaltechAUTHORS:20220322-205025270
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Official Citation:Zhihui Li, Max Gronke, Deciphering the Lyman-α emission line: towards the understanding of galactic properties extracted from Lyα spectra via radiative transfer modelling, Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 4, July 2022, Pages 5034–5051,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113985
Deposited By: George Porter
Deposited On:23 Mar 2022 14:21
Last Modified:22 Jun 2022 21:33

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